The use of few-mode optical fiber strong coupling mode division multiplexing technology is a major solution for large-capacity optical fiber communication systems, and digital signal processing can compensate for channel damage in the digital domain, providing flexibility for signal recovery and further improving transmission capacity. In this paper, the impairments which occur in the few-mode fiber system with strong mode coupling but not in single-mode fiber system are introduced. The recovery techniques for those impairments like multiple input multiple output (MIMO) equalizer, space-time coding (STC), interference cancellation, and maximum likelihood estimation as well as their principles and research results are also introduced. The shortcomings of those algorithms in terms of complexity, delay, and transmission rate are also discussed. The results show that MIMO equalization algorithm combined with STC has obvious advantages. It has important application significance in the high-capacity long-distance few-mode fiber communication system with strong mode coupling in the future.